In today's market, there is an increasing demand for the hair care products referred to as hair relaxers, which relax or straighten naturally curly or kinky hair. A hair relaxer can be a product that is applied in a hair salon by a professional or in the home by the individual consumer. One of the benefits of straightening or relaxing the curls of very curly hair is an increase in hair manageability and ease of styling.
Normally, the hair relaxing process is a chemical process which alters the chemical bonds in the hair and forms lanthionine. Hair fiber, a keratinous material, contains proteins or polypeptides, many of which are bonded together by disulfide bonds (—S—S—). A disulfide bond that is formed from the sulfhydryl groups (—SH) of two cysteine residues results in a cystine residue. While there are other types of bonds which occur between the polypeptides that make up hair, such as salt bonds, the permanent curling or the shape of the hair is essentially dependent on the disulfide bonds of cystine residues.
As a result, relaxing or straightening of hair can be achieved by disrupting the disulfide bonds of the hair fibers with an alkaline or a reducing agent. The chemical disruption of disulfide bonds by an alkaline agent is usually combined with mechanical straightening of the hair, such as combing, where straightening occurs through changing of the relative positions of opposite polypeptide chains. The reaction is subsequently terminated by rinsing and/or the application of a neutralizing composition.
The alkaline reaction is normally initiated by hydroxide ions. Not to be limited by theory, there are two reaction sequences that are predominantly used to explain the disruption of the disulfide bonds in hair by hydroxide ions, both of which result in lanthionine formation. One sequence is a bimolecular nucleophilic substitution mechanism where the hydroxide ion directly attacks the disulfide linkage, resulting in the formation of lanthionine and HOS. See Zviak, C., The Science of Hair Care, 185-186 (1986). The second is a β-elimination reaction initiated by the attack of a hydroxide ion on a hydrogen atom located on the carbon atom that is in the β-position to the disulfide bond. Id. The result is the formation of dehydroalanine, which in turn reacts with the thiol of the cysteine or the amine group of the alanine to form lanthionine and lysinoalanine. Regardless of the mechanism, the release of hydroxide ions that can penetrate the hair drives the hair relaxing process through a cystine to lanthionine transformation.
Most frequently, relaxing compositions are in the form of gels or emulsions that contain varying proportions of strong bases that are water soluble, such as sodium hydroxide, or compositions that contain slightly soluble metal hydroxides, e.g., calcium hydroxide (Ca(OH)2), that are converted in situ to soluble bases, e.g., guanidine hydroxide. Traditionally, the two main technologies used in the hair care industry for generating hydroxide to relax keratin fibers are referred to as “lye,” or sodium hydroxide, relaxers or “no lye” relaxers. The “lye” relaxers use sodium hydroxide in a concentration range of generally 1.5 to 2.5% (0.38-0.63 M) depending on the base or carrier used, the condition of the hair, and the speed of relaxation desired. Sodium hydroxide is extremely effective in straightening the hair but can result in a reduction in hair strength and, in some cases, partial or total loss of hair through breakage. Some manufacturers market lithium and potassium hydroxide relaxers as “no lye” but, while this is technically true, these relaxers still rely on the soluble hydroxides of the inorganic potassium or lithium.
Most other “no lye” relaxers operate by obtaining hydroxide from a slightly soluble source such as Ca(OH)2. For example, the slightly soluble Ca(OH)2 is mixed with guanidine carbonate to form the soluble but unstable source of hydroxide, guanidine hydroxide, and the insoluble calcium carbonate (CaCO3). The reaction is driven to completion by the precipitation of CaCO3 and is in effect substituting one insoluble calcium salt for another. Because guanidine hydroxide is fundamentally unstable, the components are separated until the time of use.
Guanidine carbonate and calcium hydroxide, however, create a different set of problems. The insoluble byproduct, CaCO3, leaves a white residue or unattractive “whitening” or “ashing” that remains in the hair since divalent metals like calcium have a relatively good affinity to keratin. A decalcifying shampoo is subsequently needed to remove the ashing.
Thus, there is a need for a process to relax keratin fibers that has the advantages of using an insoluble metal hydroxide, such as Ca(OH)2, but reduces or eliminates the problem of ashing caused by the insoluble byproduct, CaCO3.
Moreover, the use of lye relaxers or no-lye relaxers may also cause irritation to the skin of a user. Thus, there is also a need to provide an effective way of relaxing/straightening keratin fibers in a manner which is less irritating to a user's skin.